1. Field of the Invention
The present invention relates to hard disk drive (hereinafter, sometimes referred to as an HDD) generally and, in particular, to a circuit and technique for initializing the hard disk drive, and for compensating for an offset value generated in associated circuits or apparatus.
2. Description of the Related Art
Normally, in a servo control of an hard disk drive, a series of steps for initializing the hard disk drive have fatal influence on the performance of the hard disk drive. In respect to earlier hard disk drive initialization techniques, the initialization steps performed from when a head is unlatched from a parking area and moved to a data area whenever the power is applied is explained hereinafter.
Most of all, when the power is applied to the hard disk drive, at step 1, track seek and track following operations are performed for a given time period to move the head from the parking area to a specific cylinder. Hereinabove, the specific cylinder is defined to be the cylinder where an initial head is positioned on the surface of a disk to prepare for the unlatching of the head of the hard disk drive and its movement from the parking area to the data area. A control input value is produced from a position error signal (hereinafter, sometimes referred to as a PES) obtained upon the track following operation to be stored as a bias value of a first cylinder for bias calibration in a bias table. Herein, the control input value is indicative of a signal applied to a driving unit of an actuator for driving the head in a horizontal direction on the surface of the disk, that is, a voice coil motor (hereinafter, sometimes referred to as a VCM).
At step 2 following step 1, the track seek and the track following operations are performed by using the bias value generated in step 1, to thereby move the head to a second cylinder and the control input value is produced from the position error signal obtained upon the track following, the produced control input value being stored as the bias value of the second cylinder for the bias calibration in the bias table. After storing the bias values calibrated through the methods of steps 1 and 2, for example, in the bias table, a full track seek operation is performed to calibrate a torque constant Kt value as a self diagnosis function of a voice coil motor used as an actuator, thereby completing the initialization of the head in the stand-by state of the hard disk drive.
There are several disadvantages however, in performing the initialization technique of the hard disk drive as noted above. Firstly, upon track seek and track following operations of step 1, inasmuch as the head is in the off-track upon completing the track seek operation in a track seek routine due to the offset value included in an IC (integrated circuit) of a printed circuit board (hereinafter, referred to as a PCB), for example, a digital-to analog converter (hereinafter, referred to as a D/A converter), an integrator can not be operated. Also, in this case, a slip phenomenon can be generated due to off-track upon the track following operation.
Secondly, the bias value obtained by the slip phenomenon is not exact and further, has an effect on the track seek and track following operations to the corresponding track for the continuous bias calibration, so that the normal table value can not be obtained.
Thirdly, for utilizing the initial value for torque constant Kt calibration, since the initial value has each offset value for each head disk assembly, the initial torque constant Kt has an exceedingly great influence upon the bias calibration, thereby having the possibility of generating an oscillation phenomenon. In other words, there are the foregoing problems generated due to characteristic differences for each drive in the above-noted hard disk drive initialization technique.
The following references, while bearing features in common with the present invention, nevertheless do not teach or suggest the specifically recited hard disk drive initialization technique of the present invention: U.S. Pat. No. 5,500,776 to Smith, entitled Self-Calibration For Computer Disk Read/Write Offsets, U.S. Pat. No. 5,488,274 to Satoh, entitled Method For Controlling Activation Of Disk Drive Motors, U.S. Pat. No. 5,329,409 to Hampshire, entitled Correction Of Current Feedback Offset For Disc Drive Servo Systems, U.S. Pat. No. 5,305,160 to Funches et al., entitled Compensating For Variations In Torque Capability Of Voice Coil Motors, U.S. Pat. No. 5,276,569 to Even, entitled Spindle Controller With Startup Correction Of Disk Position, U.S. Pat. No. 5,227,930 to Thanos et al., entitled Head Position Recalibration For Disk Drive, U.S. Pat. No. 4,499,510 to Harding et al., entitled Precision Alignment System For Information Storage Devices, U.S. Pat. No. 4,969,059 to Voltz et al., entitled Offset Nulling System For Computer Disk Drives, and U.S. Pat. No. 4,907,109 to Seniio, entitled Magnetic Disc Drive System Having Automatic Offset And Gain Adjustment Means.